1. Field of the Invention
This invention relates to an aqueous adhesive composition suited for the bonding of various adherends, in particular, elastomers.
2. Description of the Prior Art
It is desirable for adhesives or adhesive compositions to be able to bond various materials such as metals, glasses, plastics and elastomers one another, equally and firmly. However, especially in the case of elastomers, which are various and different in types depending on, e.g., how to cure, it is difficult to develop adhesives or adhesive compositions that can bond them to other adherends equally and firmly. Even though developed, they have problems from other aspects, e.g., environmental pollution. That is, among elastomers, most natural-rubber compositions, for example, are cured using various sulfur compounds.
Elastomers such as silicone rubbers, nitrile-butadiene rubbers and fluoroelastomers are cured using polyols or peroxides, and are called non-sulfur-curable types. These non-sulfur-curable elastomers are used in seals and gaskets as high-performance special elastomers endurable to sever conditions, and are industrially very useful materials. However, even if any adhesives or adhesive compositions that can effectively bond sulfur-curable elastomers are used to bond such non-sulfur-curable elastomers, they do not necessarily exhibit equal adhesive performance. This is because commonly the non-sulfur-curable elastomers can be bonded with difficulty, compared with sulfur-curable elastomers.
Meanwhile, U.S. Pat. No. 3,022,196 discloses an example of an adhesive composition developed for use in the bonding of peroxide-curable silicone rubbers which are non-sulfur-curable elastomers. This adhesive composition has superior adhesion, heat resistance and oil resistance, but is only soluble in organic solvents because it is comprised chiefly of a mixture of water-insoluble, vinyltriethoxysilane and .gamma.-aminopropyltriethoxysilane (mixing ratio: about 5:1 in weight ratio). That is, this composition is of an organic type. Use of organic solvents, in particular, volatile solvents tends to cause environmental pollution.
Japanese Patent Publication (kokai) No.5-86335 discloses another example of an aqueous adhesive composition for use in peroxide-curable elastomers. This adhesive composition, though containing no organic solvent, is comprised chiefly of a mixture of an alkoxysilane and an unsaturated acid having corrosive properties. Hence, it has disadvantages that, when the peroxide-curable elastomers are bonded to adherends which tend to rust, such as iron and steel, bonded surfaces may corrode to attain no sufficient adhesion. Moreover, under the existing circumstances, this adhesive composition has not reached the level comparable to organic solvent type adhesive compositions in respect of adhesion to adherends, heat resistance and oil resistance.